Researchers say a recent Indonesian government report inaccurately claims that the orangutan population in the country is increasing, which could have significant implications for future conservation plans.

The report, issued by Indonesia’s Ministry of Environment and Forestry, states that the populations of 19 priority species, including orangutans, “increased by more than 10 percent” between 2015 and 2017.

But, in a letter published in the journal Current Biology on Monday, researchers say that that assertion “is in strong contrast” to many recently published and peer-reviewed scientific studies on the status of the three orangutan species.

Researchers say a recent Indonesian government report inaccurately claims that the orangutan population in the country is increasing, which could have significant implications for future conservation plans.

The report, issued by Indonesia’s Ministry of Environment and Forestry with support from the UN’s Food and Agricultural Organization and Norway’s International Climate and Forest Initiative, states that the populations of 19 priority species, including orangutans, “increased by more than 10 percent” between 2015 and 2017.

According to Erik Meijaard, who coordinates the Borneo Futures initiative and is the lead author of the letter, orangutan numbers are in decline, not increasing as the Indonesian government report contends.

“The government monitoring data do indeed support such an increase, so that would justify the government’s claim. But, as we point out, the monitoring methods are flawed for a variety of reasons,” Meijaard told Mongabay. “Also, I find it strange that the government authorities and the NGO groups working with the government simply ignore a number of peer reviewed papers that document high rates of population decline, forest loss, and killing.”

Meijaard and his co-authors cite a number of flaws in the Indonesian government’s methodology for monitoring impacts on orangutan populations and the conclusions drawn from that monitoring. For instance, the government’s assessment relies on nine monitoring sites, including national parks, where a population of 1,153 orangutans was established in 2015. The government estimated that the populations at these nine sites had more than doubled to 2,451 individual orangutans by 2016. The researchers write in the letter, however, that it is “biologically impossible for an orangutan population to double its size in a year.”

“It is obvious from the orangutan’s biology that doubling a population in one year, as reported from the monitoring sites, is impossible, and should have alerted the government that something may be wrong about their data,” Meijaard said. “Orangutans are not rabbits.”

Orangutans in the wild in Indonesia. Photo Credit: HUTAN-KOCP.

Other issues with the Indonesian government’s methodology, Meijaard and colleagues note, include the fact that some of the sampling sites are used for orangutan introductions or translocations, meaning that any increase in the numbers of orangutans at those sites was likely the result of removing animals from a non-monitored population — thus leading to zero net change in the overall numbers of orangutans.

Also, the government’s nine sampling sites represent less than 5 percent of the Bornean and Sumatran orangutans’ ranges, and misses the Tapanuli orangutan’s range altogether, the researchers write. They add: “Furthermore, all monitoring sites are within protected areas, whereas the majority of orangutans occur in non-protected lands. It is thus scientifically unjustified to extrapolate population trends from these sampling sites to the total range of all three species.”

Mongabay reached out to Indonesia’s Minister of Environment and Forestry as well as other government officials, but requests for comment were declined.

There is a solid research base to bolster the Current Biology letter writers’ assertion that all three orangutan species are in fact on the decline. A 2018 study determined that more than 100,000 Bornean orangutans had been lost in the past 16 years, for instance, while a 2017 study found that the Bornean orangutan population has declined by more than 25 percent over the past decade.

Meanwhile, the IUCN reports that forest loss data indicate that habitat for both the Sumatran orangutan and the Tapanuli orangutan was reduced by 60 percent between 1985 and 2007. A 2016 study predicted that continued forest loss could result in the loss of as many as 4,500 Sumatran orangutan individuals by 2030.

“For the Sumatran orangutan, the population decline is mostly estimated on the basis of forest loss — no forest generally means no orangutans, so that is not something the government can deny,” Meijaard said. “For the third species, the Tapanuli orangutan, the population trends are based on habitat loss estimates and reports of killing.”

Poaching and retaliatory killing of orangutans is one of the chief threats the species face, Meijaard added: “Killing is an important factor that drives declines in all three species, especially on Borneo where studies show it to be the biggest driver of population decline.” Yet “Currently orangutan conservation groups (government, NGO, private sector) are not focusing sufficiently on the key threat, which is killing — strategies that reduce killing need to be stepped up.”

The Indonesian government is currently in the process of developing a new 10-year action plan for orangutan conservation, and Meijaard said that the government’s assessments of orangutan populations could make a crucial difference in how that plan turns out. “If there was a population increase in the previous 10 years, then the plan can stay the same,” he said. “But if there was a major population decrease, as found by our studies, then a radically different approach to conservation is needed, and the government needs to incorporate these new strategies into their plan.”